Superabrasive particle synthesis with growth control

ABSTRACT

An improved method for synthesizing superabrasive particles provides high quality industrial superabrasive particles with high yield and a narrow size distribution. The synthesis method can include forming a growth precursor of a substantially homogeneous mixture of raw material and catalyst material or layers of raw material and metal catalyst. The growth precursor can have a layer of adhesive over at least a portion thereof. A plurality of crystalline seeds can be placed in a predetermined pattern on the layer of adhesive. The growth precursor can be maintained at a temperature and pressure at which the superabrasive crystal is thermodynamically stable for a time sufficient for a desired degree of growth. Advantageously, the patterned placement of crystalline seeds and disclosed processes allow for production of various morphologies of synthetic diamonds, including octahedral and cubic diamonds, and improved growth conditions generally. As a result, the grown superabrasive particles typically have a high yield of high quality particles and a narrow distribution of particle sizes.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/175,017, filed Jul. 5, 2005, which is a continuation-in-part of U.S.patent application Ser. No. 10/926,576, filed Aug. 25, 2004, which is acontinuation-in-part of U.S. patent application Ser. No. 10/791,300,filed Mar. 1, 2004, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/259,168, filed Sep. 27, 2002, which is acontinuation-in-part of U.S. patent application Ser. No. 09/935,204,filed Aug. 22, 2001, now issued as U.S. Pat. No. 6,679,243, which is acontinuation-in-part of U.S. patent application Ser. No. 09/399,573,filed Sep. 20, 1999, now issued as U.S. Pat. No. 6,286,498, which is acontinuation-in-part application of U.S. patent application Ser. No.08/835,117, filed Apr. 4, 1997, now issued as U.S. Pat. No. 6,039,641,and of U.S. patent application Ser. No. 08/832,852, filed Apr. 4, 1997,now abandoned, all of which are incorporated herein by reference.Additionally, this application is a continuation of U.S. patentapplication Ser. No. 10/926,574, filed Aug. 25, 2004, which is acontinuation-in-part of U.S. patent application Ser. No. 10/791,300,filed Mar. 1, 2004, which is a continuation-in-part of U.S. patentapplication Ser. No. 10/259,168, filed Sep. 27, 2002, which is acontinuation-in-part of U.S. patent application Ser. No. 09/935,204,filed Aug. 22, 2001, now issued as U.S. Pat. No. 6,679,243, which is acontinuation-in-part of U.S. patent application Ser. No. 09/399,573,filed Sep. 20, 1999, now issued as U.S. Pat. No. 6,286,498, which is acontinuation-in-part application of U.S. patent application Ser. No.08/835,117, filed Apr. 4, 1997, now issued as U.S. Pat. No. 6,039,641,and of U.S. patent application Ser. No. 08/832,852, filed Apr. 4, 1997,now abandoned, all of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to methods of synthesizingsuperabrasive particles. Accordingly, the present invention involves thefields of chemistry, metallurgy, and materials science.

BACKGROUND OF THE INVENTION

Diamond and cubic boron nitride (cBN) particles have found widespreaduse as superabrasives in a variety of abrading and cutting applications.The worldwide consumption of diamond particles currently exceeds 400metric tons. Common tools which incorporate superabrasive particlesinclude cutting tools, drill bits, circular saws, grinding wheels,lapping belts, polishing pads, and the like. In general, diamond gritscan be classified into three distinct size ranges: coarse mesh saw grits(U.S. mesh 18 to 60 or 1 mm to 0.23 mm) for sawing applications, mediumsized grinding grits (U.S. mesh 60 to 400, 230 microns to 37 microns)for grinding applications, and fine powder of micron diamond (U.S. mesh<400 mesh) for polishing applications.

Among diamond superabrasives, saw diamond has the largest particle sizeat about 18 to 60 mesh. High quality saw diamonds are generally euhedralhaving fully grown crystallographic faces. Further, high quality sawdiamond should have very few defects or inclusions. Standardapplications for saw diamonds require high quality diamonds. This is atleast partially due to the high impact force encountered during cutting,particularly at high speeds. In contrast, smaller diamond particles,i.e. 60 to 400 mesh or 0.25 mm to 37 μm, such as those used in grindingwheels, create scratches in the surface which gradually removes materialfrom a workpiece. In such grinding applications, the impact force istypically much less than for cutting applications. Thus, commerciallysatisfactory smaller diamonds can be produced with less concern forflaws and impurities than is generally acceptable for larger diamondssuch as saw diamonds.

Superabrasives are typically formed under ultrahigh pressure, e.g.,about 5.5 GPa and high temperature, e.g., 1300° C. The quality ofdiamond grits is typically controlled by the growth rate. A slowergrowth rate can allow for more complete formation of the crystalmorphology and a lower amount of interior defects. High quality,well-crystallized diamond grits will exhibit higher impact strengthsuitable for more aggressive sawing action. The amount of defects (e.g.metal inclusion) will also affect the thermal stability of the diamondgrit. A less included diamond can withstand a higher processingtemperature (e.g. 1000° C.) typically used for making diamond toolswithout deterioration. Diamonds having a lower amount of inclusions canalso wear slower at the cutting tips where heat is generated.

Diamond grits are typically grown by converting graphite to diamondunder catalytic action of a molten metal. The molten metal also servesas a solvent of carbon. Typical catalysts used to synthesis diamondinclude iron, nickel, cobalt, manganese or their alloys. The growth rateof diamond is controlled by pressure and temperature. Typically, thelower the over-pressure required to make diamond stable and/or the lowerthe over-temperature needed to melt the catalyst metal, the slower thegrowth rate. For example, to grow saw grits in a molten alloy of ironand nickel of Invar composition (Fe65-Ni35), the pressure is about 5.2GPa and temperature is about 1270° C.

Once the growth rate is determined for synthesizing a certain quality ofgrade of diamond, its size can be determined by the growth time. Becausethe saw grits are much larger than grinding grits, they require muchlonger growth time. For example, the growth of 30/40 mesh may require 45minutes; and 40/50 mesh, 25 minutes. In contrast, the growth of 100/120mesh may need 2 minutes; and 200/230, 1 minute. Micron diamond istypically produced by pulverizing larger diamond, particularly, largerdiamonds with a large amount of defects.

As the time for diamond growth increases, the more difficult it is tocontrol pressure and temperature. However, under ultrahigh pressureconditions during crystal growth, the pressure tends to continuallydecay due to the volume contraction associated with diamond formation.Further, temperatures within the growth regions can increase due toincreases in electrical resistance associated with the diamondformation. Hence, it is very difficult to maintain optimal conditions ofpressure and temperature for homogeneous growth of diamond grits. Sawdiamond grits are typically grown under ultrahigh pressure over a muchlonger time, e.g., 40 minutes than that required to grow smallergrinding grits, e.g., about 1 minute. Consequently, saw diamond gritsare very difficult to grow, particularly those having high quality. Sawgrits with high impact strength are characterized by a euhedral crystalshape and very low inclusions of either metal or graphite. Hence, verytight controls of pressure and temperature are required over extendedperiods of time to produce high quality diamonds.

These difficulties partially account for the abundance of companieswhich can grow saw grits, while very few companies are capable ofgrowing high grade saw grits having larger sizes. As a result, very fewcompanies can master the technology of growing coarse saw grits, inparticular, those with high quality, high impact strength, and highthermal stability.

Typical methods for synthesizing larger high quality diamonds involveensuring uniformity of raw materials such as graphite and metal catalystand carefully controlling process temperature and pressures. Highpressure high temperature (HPHT) processes used in diamond growth canemploy reaction volumes of over 200 cm³. Most often, the graphite todiamond conversion in the reaction volume can be up to about 30%.Unfortunately, typical processes also result in the crystals havingexternal flaws, e.g., rough surfaces, and undesirable inclusions, e.g.,metal and carbon inclusions. Therefore, increased costs are incurred insegregating acceptable high strength diamonds from weaker, poor qualitydiamonds.

One major factor to consider in diamond synthesis of high grade sawdiamonds is providing conditions such that nucleation of diamond occursuniformly and nearly simultaneously. Random nucleation methods typicallyallow some regions of raw materials to be wasted while other regions aredensely packed with diamond crystals having a high percentage ofdefects. Some diamond synthesis methods have improved nucleationuniformity somewhat; however, during diamond growth local changes inpressure can occur. If heating is accomplished by passing electricalcurrent directly through the reaction cell, then diamond growth can alsointerfere with the electrical current used to control heating. Theresults of such interference are non-uniformities and fluctuations inthe temperature and pressure gradients across the reaction cell and thusa wide distribution of crystal sizes, crystal shapes, and inclusionlevels. Despite these difficulties, by providing highly homogeneousstarting materials and carefully controlling process conditions, thevolume efficiency of the reaction cell is still typically less than 2 to3 carats per cubic centimeter. This marginal yield still wastes largeamounts of raw materials, reduces production efficiencies, and leavesconsiderable room for improvement.

Other methods for synthesizing large industrial diamond particlesinclude forming layers of solid disks of graphite and/or catalyst.Diamond nucleation then occurs at the interface between graphite andcatalyst layers. However, such materials are intrinsicallyheterogeneous. For example, the firing temperature for graphite rodsthat are cut into disks can vary from region to region, thus affectingthe microstructure and composition of the disk. Further, duringmechanical formation of graphite into a rod, the graphite microstructurecan change, e.g., the outer regions exhibit a skin effect duringextrusion. As a result, graphite disks tend to have regions which varyin porosity, degree of graphitization, ash content, and the like.Similarly, catalyst disks have varying alloy composition as metal atomsand crystal structure tend to segregate during cooling. Additionally,during extrusion and mechanical forming processes the alloy compositionin various regions changes even further. As a result, localconcentrations and properties of graphite and catalyst metals can varyby several percent across solid disks. Diamonds grown under suchconditions tend to nucleate at different times and experience varyinggrowth rates, thus producing diamonds having a wide size distributionand increasing the number of flawed diamonds due to intergrowth,overgrowth, i.e. fast growth rates, and uneven growth, i.e. asymmetricgrowth, as shown in FIGS. 19A, 19B, and 22.

Recently, efforts have been made in using powdered materials to furtherincrease yields of industrial diamond particles. These methods attemptto uniformly mix graphite and catalyst powders to achieve improveddiamond nucleation. However, diamond nucleation still occurs randomly,i.e. broad size distribution, but somewhat uniformly throughout thepowder under HPHT conditions, as shown in FIG. 23. Such methods have metwith some success and have resulted in improved yields of up to 3carat/cm³. Further, yields of high quality diamond of specific sizeshave also improved up to five times over those achievable usingconventional layered disk methods. However, powdered mixture methods canbe difficult to control. For example, the density of graphite and metalcatalyst materials differ significantly, making uniform mixing verydifficult. In addition, powdered mixture methods generally require evenmore strict control of process conditions than in layered methods.

SUMMARY OF THE INVENTION

It has been recognized by the inventor that it would be advantageous todevelop a method for synthesizing superabrasive particles which provideshigh quality industrial superabrasive particles with a high yield andnarrow size distribution.

In one aspect, the present invention resolves the problems set forthabove by providing a method for synthesizing superabrasive particles.The above method can include forming at least a portion of a growthprecursor. The growth precursor can include a raw material and aparticulate catalyst material. Crystalline seeds can be arranged in apredetermined pattern on a layer of adhesive. The layer of adhesive cancoat at least a portion of the growth precursor. In some embodiments,the growth precursor can be a substantially homogenous mixture ofparticulate raw material and particulate catalyst material.Alternatively, the growth precursor can comprise layers of raw materialand catalyst material.

The layer of adhesive can be coated over the growth precursor by anynumber of methods such as, but not limited to, spraying, film coating,spin coating, and the like.

The method of the present invention can be applied to formation ofsuperabrasives such as diamond and cubic boron nitride (cBN). In eithercase, the crystalline seed can be diamond seed, cBN seed, SiC seed, orcombinations thereof.

Suitable catalyst materials for diamond synthesis can include carbonsolvents such as Fe, Ni, Co, Mn, Cr, and alloys thereof. Alloys of ironand nickel have proven useful in connection with the present inventionand are readily commercially available. Catalyst materials suitable forcBN synthesis can include alkali, alkali earth metal, and compoundsthereof.

The composition of the raw material can depend on the type ofsuperabrasive being synthesized. Diamond synthesis typically involvesusing a carbon source. In another detailed aspect of the presentinvention, the carbon source can be primarily graphite. Further, inaccordance with the present invention, the degree of graphitization canpreferably be greater than 0.50. The carbon source can be formed as aparticulate layer or as a solid plate of graphite. Similarly, the rawmaterial suitable for cBN synthesis can be a hexagonal boron nitridesource.

In another aspect of the present invention, the growth precursor caninclude a plurality of alternating raw material and catalyst layers.Depending on the reaction volume of the HPHT apparatus used, the numberof layers can vary from a single layer to thirty layers or more. In yetanother detailed aspect, the growth precursor can include a plurality ofparticulate catalyst layers each having a plurality of crystalline seedsplaced in a predetermined pattern. These predetermined patterns caninvolve crystalline seeds of different sizes or type. Further, thepredetermined pattern can involve crystalline seed placement within eachlayer and specific patterns with respect to patterns of crystallineseeds among layers, which patterns can differ from layer to layer.

Appropriate growth conditions can be maintained using any number ofknown HPHT apparatuses such as, but not limited to, belt apparatus,cubic press, toroidal apparatus, sliding anvils, split sphere, splitdie, and the like. Using such devices, the growth precursor can bemaintained at a temperature and pressure at which diamond or cBN isthermodynamically stable for a time sufficient for growth of thesuperabrasive. Advantageously, placing the crystalline seeds at leastpartially in a particulate catalyst layer provides highly uniform growthconditions which are less demanding than is required in typicalsynthesis processes. Thus, the placement of crystalline seeds in apredetermined pattern helps to improve uniformity of crystal growth,nucleation times, and reduces intergrowth of crystals and non-growingregions, while providing a particulate catalyst layer aids in increasinguniformity of crystalline growth with few defects.

In accordance with yet another aspect of the present invention, thecrystalline seeds can be placed in a predetermined pattern using anynumber of methods. One method involves placing a template having apattern of apertures upon the adhesive layer. Each of the apertures canbe configured to receive a single crystalline seed. The apertures canthen be filled with the crystalline seeds. Optionally, the crystallineseeds can then be pressed at least partially into the growth precursor.

In an alternative embodiment, a transfer sheet can be used to place thecrystalline seeds in a predetermined pattern on the adhesive layer. Instill another alternative embodiment, a vacuum chuck can be used toorient and place the crystalline seeds in the predetermined pattern. Theadhesive layer can preferably be an organic binder which minimizesshifting or movement of the crystalline seeds during subsequentmanipulation of the growth precursor. Such a method can reducedisruption of the predetermined pattern when the template is removed,when pressure is applied to the crystalline seeds, and/or when thegrowth precursor is moved during processing, e.g. oriented adhesive sidedown.

In accordance with yet another aspect of the invention, the crystallineseeds can be grown having various morphologies. Diamond growth can becontrolled by preferentially growing diamond to existing crystal facesthrough careful temperature control under pressure, resulting in variousmorphologies including octahedral and cubic.

The grown superabrasives of the present invention have a high yield ofhigh quality diamond particles and a narrow distribution of diamondsizes. Typically, yields of diamond particles can range from about 30%to about 80% conversion of carbon to diamond can be expected. Further,the percent of high quality diamond can range from 50% to about 90% ofthe total yield. As a further example of the effectiveness of thepresent invention, the grown diamonds of the present invention can havea narrow size distribution with a standard deviation less than half ofconventional methods described above. Also, the grown diamonds of thepresent invention can have significantly fewer inclusions.

There has thus been outlined, rather broadly, various features of theinvention so that the detailed description thereof that follows may bebetter understood, and so that the present contribution to the art maybe better appreciated. Other features of the present invention willbecome more clear from the following detailed description of theinvention, taken with the accompanying claims, or may be learned by thepractice of the invention.

Additional features and advantages of the invention will be apparentfrom the detailed description which follows, taken in conjunction withthe accompanying drawings, which together illustrate, by way of example,features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of a raw material layer and particulate catalystlayer having a template thereon in accordance with an embodiment of thepresent invention;

FIG. 2A is a top view of a template in accordance with an embodiment ofthe present invention;

FIG. 2B is a top view of a template in accordance with anotherembodiment of the present invention;

FIG. 3 is a side view of the assembly of FIG. 1 having crystalline seedsplaced in a predetermined pattern in accordance with an embodiment ofthe present invention;

FIG. 4 is a side view of pressing the crystalline seeds into thecatalyst layer in accordance with an embodiment of the presentinvention;

FIG. 5 is a side view of a growth precursor in accordance with anembodiment of the present invention;

FIG. 6 is a side view of a multi-layered growth precursor in accordancewith an embodiment of the present invention;

FIG. 7 is a side view of a multi-layered growth precursor in accordancewith an alternative embodiment of the present invention;

FIGS. 8A and 8B are photomicrographs of nickel coated diamond seeds foruse in one embodiment of the present invention;

FIG. 9A is a perspective view of a single octahedral (111) face ofdiamond;

FIG. 9B is a perspective view of a single carbon atom having a singleunbonded electron;

FIG. 9C is a perspective view of a puckered graphitic plane;

FIG. 10A is a perspective view of graphitic planes;

FIG. 10B is a perspective view of diamond-like carbon formed from thegraphitic planes of FIG. 10A;

FIG. 10C is a perspective view of diamond formed from the diamond-likecarbon of FIG. 10B;

FIG. 11A is a perspective view of a single cubic (100) face of diamond;

FIG. 11B is a perspective view of a single carbon atom having twounbonded electrons;

FIG. 11C is a perspective view of diamond grown along the cubic face;

FIG. 12A is a side cross-sectional view of a growing diamond having acontinuous catalyst envelope in accordance with one embodiment of thepresent invention;

FIG. 12B is an expanded side cross-sectional view of feature 36 showinga growing cubic face of diamond in accordance with one embodiment of thepresent invention;

FIG. 12C is an expanded side cross-sectional view of feature 38 showinga growing octahedral face of diamond in accordance with one embodimentof the present invention;

FIG. 13A is a side cross-sectional view of a growing diamond dominatedby growth on the octahedral faces to form a more cubic diamond inaccordance with one embodiment of the present invention;

FIG. 13B is a side cross-sectional view of a growing diamond dominatedby growth on the cubic faces to form a more octahedral diamond inaccordance with one embodiment of the present invention;

FIG. 14 is a series of crystal morphologies of diamond and correspondinggrowth parameters;

FIG. 15 is a photomicrograph of a number of cubo-octahedral diamonds;

FIG. 16 is a graph illustrating a number of growth considerations andeffects in using the methods of the present invention;

FIG. 17 shows a side view of a portion of a multi-layered assembly suchas shown in FIG. 6 after HPHT processing and identifying various aspectsof crystalline growth in accordance with an embodiment of the presentinvention;

FIG. 18 is a photomicrograph of a grown diamond assembly in accordancewith the present invention, which exhibits highly uniform sizedistribution and uniform crystal shapes.

FIG. 19A is a photomicrograph of a grown diamond assembly in accordancewith the prior art, which exhibits non-uniform size distribution andnon-uniform crystal shapes;

FIG. 19B is a photomicrograph of unsorted and unsized diamonds recoveredfrom the assembly of FIG. 19A;

FIG. 20A is a photomicrograph of a grown diamond assembly in accordancewith one embodiment of the present invention, which exhibits highlyuniform size distribution and uniform crystal shapes;

FIG. 20B is a photomicrograph of unsorted and unsized cubo-octahedraldiamonds recovered from the assembly of FIG. 20A;

FIG. 21A is a photomicrograph of a grown diamond assembly in accordancewith one embodiment of the present invention, which exhibits highlyuniform size distribution and uniform crystal shapes;

FIG. 21B is a photomicrograph of unsorted and unsized diamonds recoveredfrom the assembly of FIG. 21A which are predominantly octahedraldiamonds;

FIG. 22 is a photomicrograph of a conventional diamond assembly grownfrom an alternating plate method which highlights the non-uniform sizedistribution and non-uniform crystal shapes; and

FIG. 23 is a photomicrograph of a diamond assembly grown using knownpowdered methods which show some improvement over conventional methods,however still suffer from somewhat non-uniform size distributions andnon-uniform crystal shapes.

FIG. 24 is a photograph of a post-growth mass having offset patterns ofdiamond crystals as described in Example 13.

FIG. 25 is a photomicrograph of the post-growth mass of diamondparticles having a predominantly cubic morphology and an average size ofabout 500 μm in accordance with Example 13.

FIG. 26 is an additional photomicrograph of the post-growth mass of FIG.24 showing cubic diamonds prior to recovery.

FIG. 27 illustrates a collection of unsorted diamonds having apredominantly cubic morphology produced from Example 13.

DETAILED DESCRIPTION

Reference will now be made to the exemplary embodiments illustrated inthe drawings, and specific language will be used herein to describe thesame. It will nevertheless be understood that no limitation of the scopeof the invention is thereby intended. Alterations and furthermodifications of the inventive features, process steps, and materialsillustrated herein, and additional applications of the principles of theinventions as illustrated herein, which would occur to one skilled inthe relevant art and having possession of this disclosure, are to beconsidered within the scope of the invention. It should also beunderstood that terminology employed herein is used for the purpose ofdescribing particular embodiments only and is not intended to belimiting.

A. Definitions

In describing and claiming the present invention, the followingterminology will be used.

The singular forms “a,” “an,” and “the” include plural referents unlessthe context clearly dictates otherwise. Thus, for example, reference to“a matrix material” includes reference to one or more of such materials,and reference to “an alloy” includes reference to one or more of suchalloys.

As used herein, “particulate” when used with respect to layers indicatesthat the layer is formed of particulates. Typically, particulate layersof the present invention can be loose powder, packed powder, orcompacted powder having substantially no sintered particles. Theseparticulate layers can be porous or semi-porous compacts. Compactedparticulate layers can be formed using any known compaction process suchas, but not limited to, wet or dry cold compaction such as coldisostatic pressing, die compacting, rolling, injection molding, slipcasting, and the like. The particulate materials used in the presentinvention such as graphite and metal catalyst powders can be preferablyhandled and stored in an inert environment in order to prevent oxidationand contamination.

As used herein, “substantially free of” or the like refers to the lackof an identified element or agent in a composition. Particularly,elements that are identified as being “substantially free of” are eithercompletely absent from the composition, or are included only in amountswhich are small enough so as to have no measurable effect on thecomposition.

As used herein, “predetermined pattern” refers to a non-random patternthat is identified prior to formation of a precursor, and whichindividually places or locates each crystalline seed in a definedrelationship with the other crystalline seeds. For example, “placingdiamond seeds in a predetermined pattern” would refer to positioningindividual particles at specific non-random and pre-selected positions.Further, such patterns are not limited to uniform grid or offsethoneycomb patterns but may include any number of configurations based onthe growth conditions and materials used.

As used herein, “uniform grid pattern” refers to a pattern of diamondparticles that are evenly spaced from one another in all directions.

As used herein, “substrate” refers to a solid metal material. While manysolid metal materials may be a product of metal particulate sintering orconsolidation, it is to be understood, that as used herein, “substrate”does not include powdered or particulate metal materials that have notyet been sintered or consolidated into a solid mass or form.

As used herein, “alloy” refers to a solid or liquid solution of a metalwith a second material, said second material may be a non-metal, such ascarbon, a metal, or an alloy which enhances or improves the propertiesof the metal.

As used herein, “crystalline seeds” refer to particles which serve as astarting material for growth of a larger crystalline particle. As usedherein, crystalline seeds typically include diamond seeds, cBN seeds,and SiC seeds. For example, growth of superabrasive diamond is commonlyachieved using diamond seeds; however cBN and/or SiC seeds can also beused to grow superabrasive diamond. Similarly, cBN can be grown usingdiamond, cBN, and/or SiC seeds.

As used herein, “diamond seeds” refer to particles of either natural orsynthetic diamond, super hard crystalline, or polycrystalline substance,or mixture of substances and include but are not limited to diamond,polycrystalline diamond (PCD). Diamond seeds are used as a startingmaterial for growing larger diamond crystals and help to avoid randomnucleation and growth of diamond.

As used herein, “superabrasive particles” refers to particles suitablefor use as an abrasive and include diamond and cBN particles.

As used herein, “precursor” refers to an assembly of crystalline seeds,particulate catalyst layer, and a raw material layer. A precursordescribes such an assembly prior to the HPHT growth process. Suchunsintered precursors are sometimes referred to as a “green body.”

As used herein, “plate” refers to a mass of material which is partiallysintered, completely sintered, or non-porous crystalline in structure.This is in distinction to a compact or pressed powder which includesparticulates which are substantially unsintered. Plates can typically becircular or disk shaped; however, other shapes which are functional canalso be used, e.g., square.

As used herein, “degree of graphitization” refers to the proportion ofgraphite which has graphene planes having a theoretical spacing of 3.354angstroms. Thus, a degree of graphitization of 1 indicates that 100% ofthe graphite has a basal plane separation (d₍₀₀₀₂₎) of graphene planes,i.e. with hexagonal network of carbon atoms, of 3.354 angstroms. Ahigher degree of graphitization indicates smaller spacing of grapheneplanes. The degree of graphitization, G, can be calculated usingEquation 1.G=(3.440−d ₍₀₀₀₂₎)/(3.440−3.354)  (1)Conversely, d₍₀₀₀₂₎ can be calculated based on G using Equation 2.d ₍₀₀₀₂₎=3.354+0.086(1−G)  (2)

Referring to Equation 1, 3.440 angstroms is the spacing of basal planesfor amorphous carbon (L_(c)=50 Å), while 3.354 angstroms is the spacingof pure graphite (L_(c)=1000 Å) that may be achievable by sinteringgraphitizable carbon at 3000° C. for extended periods of time, e.g., 12hours. A higher degree of graphitization corresponds to largercrystallite sizes, which are characterized by the size of the basalplanes (L_(a)) and size of stacking layers (L_(c)). Note that the sizeparameters are inversely related to the spacing of basal planes. Table 1shows crystallite properties for several common types of graphite. TABLE1 Graphite Type d₍₀₀₂₎ L_(a) (Å) L_(c) (Å) I₁₁₂/I₁₁₀ Natural 3.355 1250375 1.3 Low Temp (2800° C.) 3.359 645 227 1.0 Electrode 3.360 509 1841.0 Spectroscopic 3.362 475 145 0.6 High Temp (3000° C.) 3.368 400 0.9Low Ash 3.380 601 180 0.8 Poor Natural 3.43 98 44 0.5

As used herein, “aperture” refers to an opening through a templatesurface which has a predetermined size and shape depending on theintended application. For example, the aperture size may be designed toaccommodate a plurality of crystalline seeds of a given mesh size.However, it is most often desirable to design the apertures such thatonly one crystalline seed is accommodated by each aperture.

As used herein, “inclusion” refers to formation of carbon or metaldeposits instead of diamond at the interface between a growth surface ofthe diamond and the surrounding material. Inclusions are most oftenformed by the presence of substantial amounts of carbon at the growthsurface of the diamond and/or inadequate control of temperature andpressure conditions during HPHT growth. Similar inclusions and defectscan also be formed during cBN synthesis.

As used herein, “euhedral” means idiomorphic or a crystal having anunaltered natural shape containing natural crystallographic faces.

As used herein, “octahedral” refers to a crystal morphology whereincrystallographic faces are dominantly the (111) plane. Octahedraldiamond crystals typically have eight triangular faces as shown in FIG.14 (far right) and FIG. 21B (predominantly octahedral diamonds).

As used herein, “upon” refers to either actual physical contact orsufficient proximity to achieve the desired effect. For example, placinga template upon the growth precursor can allow for a small space betweenthe growth precursor and the template such that particle placement inthe desired pattern is still realized. Typical process conditions canallow for actual physical contact.

As used herein, a plurality of items, structural elements, compositionalelements, and/or materials may be presented in a common list forconvenience. However, these lists should be construed as though eachmember of the list is individually identified as a separate and uniquemember. Thus, no individual member of such list should be construed as ade facto equivalent of any other member of the same list solely based ontheir presentation in a common group without indications to thecontrary.

Concentrations, amounts, and other numerical data may be presentedherein in a range format. It is to be understood that such range formatis used merely for convenience and brevity and should be interpretedflexibly to include not only the numerical values explicitly recited asthe limits of the range, but also to include all the individualnumerical values or sub-ranges encompassed within that range as if eachnumerical value and sub-range is explicitly recited.

For example, a numerical range of about 1 to about 4.5 should beinterpreted to include not only the explicitly recited limits of 1 toabout 4.5, but also to include individual numerals such as 2, 3, 4, andsub-ranges such as 1 to 3, 2 to 4, etc. The same principle applies toranges reciting only one numerical value, such as “less than about 4.5,”which should be interpreted to include all of the above-recited valuesand ranges. Further, such an interpretation should apply regardless ofthe breadth of the range or the characteristic being described.

B. The Invention

Reference will now be made to the drawings in which the various elementsof the present invention will be given numeral designations and in whichthe invention will be discussed. It is to be understood that thefollowing description is only exemplary of the principles of the presentinvention, and should not be viewed as narrowing the appended claims.

The present invention includes a method for synthesizing superabrasiveparticles and controlling nucleation and growth during superabrasiveparticle synthesis. Generally, the methods of the present invention canbe used to form either diamond or cBN superabrasive particles fromcorresponding crystalline seeds. However, it will be understood that theprinciples of the present invention can also be useful for production ofother crystalline particles.

Growth Precursors

Referring now to FIG. 1, a raw material layer 12 can be formed. The rawmaterial layer can be provided as a particulate layer or as a solidplate. In one aspect of the present invention, the raw material layercan be a particulate layer. In one embodiment of the present invention,the raw material layer can be provided as a loose powder. The loosepowder can be placed in a mold and optionally pressed using any knownpressing technique. For example, the powder can be pressed using coldisostatic pressing at about 200 MPa to achieve a porosity of from about8% to about 15%, although porosities of less than about 30% aretypically satisfactory. Using particulate layers can provide ease ofplanting crystalline seeds therein and avoid formation of large voidsaround the crystalline seeds.

The raw material layer can include any materials which are capable ofproviding raw materials for growth of a desired superabrasive particle.Specifically, a carbon source can be used for diamond growth, while alow pressure-phase boron nitride such as hexagonal boron nitride can beused for cBN growth. Under diamond growth conditions, the carbon sourcelayer can comprise a carbon source material such as graphite, amorphouscarbon, diamond powder, and the like. In one aspect of the presentinvention, the carbon source layer can comprise graphite. Although avariety of carbon source materials can be used, graphite generallyprovides good crystal growth and improves homogeneity of the growndiamonds. When graphite is used as the carbon source material,preferably the carbon source material comprises at least about 85 wt %graphite. For embodiments wherein the graphite is formed as aparticulate layer, suitable graphite powder can typically be from about1 μm to about 1 mm. In one detailed aspect of the present invention, thegraphite can have a degree of graphitization of greater than 0.50.Preferably, the graphite can have a degree of graphitization of fromabout 0.75 to about 1, and in some cases greater than about 0.80.However, the degree of graphitization is most preferably from about 0.85to about 1. Experiments have shown that a higher degree ofgraphitization corresponds to larger crystallite sizes and improvedgrown diamond quality and uniformity. Diamond is typically formedthrough puckering and bending of graphene planes in the presence ofmolten catalyst metal. Therefore, diamond formation can be improved byproviding graphite having a high degree of graphitization.

In another aspect of the present invention, a particulate catalyst layer14 can be formed adjacent the raw material layer 12. The particulatecatalyst layer can be formed of metal catalyst powder. The metalcatalyst layers of the present invention can be formed as a loosepowder, porous compact or other substantially non-sintered mass. Loosepowder can be used directly by placing the powder in a suitable moldadjacent to the raw material layer. This loose powder can be optionallypressed using known pressing technologies to form a disk. Alternatively,the metal catalyst powder can be formed into a disk and thensubsequently placed adjacent the raw material layer.

In a preferred embodiment, the particulate catalyst layer contains nobinder, no oils, and no organic materials. Further, the particulatecatalyst layers of the present invention can consist essentially ofmetal catalyst powder. The presence of organic materials during thegrowth process can cause undesirable flaws and non-uniformities in thegrown superabrasive crystal structures. Providing a particulate catalystlayer allows for crystalline seeds to be easily embedded in the catalystlayer, as described in more detail below. Care should be taken whenhandling such particulate layers, since the absence of organic bindersand the like tends to make the assemblies and disks more brittle than ifan organic binder was included. Therefore, in some embodiments of thepresent invention, it can be desirable to use a solid plate as the rawmaterial layer to provide additional mechanical support to the assembly.In an optional embodiment, raw material layers and catalyst layers canbe pressed together to form a convenient supply of two-layer assembliesfor use in the methods of the present invention. In one aspect of thepresent invention, the particulate catalyst layer can have a porosity ofless than about 33%.

In one detailed aspect of the present invention, the catalyst layer cancomprise a catalyst material which is suitable for growth of the desiredsuperabrasive particle. Catalyst materials suitable for diamondsynthesis can include metal catalyst powder comprising any metal oralloy which is a carbon solvent capable of promoting growth of diamondfrom carbon source materials. Non-limiting examples of suitable metalcatalyst materials can include Fe, Ni, Co, Mn, Cr, and alloys thereof.Several common metal catalyst alloys can include Fe—Ni, e.g., INVARalloys, Fe—Co, Ni—Mn—Co, and the like. Currently preferred metalcatalyst materials are Fe—Ni alloys, such as Fe-35Ni, Fe-31Ni-5Co,Fe-30Ni, and other INVAR alloys, with Fe-35Ni being most preferred andmore readily available. Generally, suitable Fe—Ni alloys can have anickel content which varies from about 10 wt % to about 50 wt %. Inaddition, the catalyst materials under diamond synthesis can includeadditives which control the growth rate of diamond, i.e. via suppressingcarbon diffusion, and also prevent excess nitrogen and/or oxygen fromdiffusing into the diamond. Suitable additives can include Mg, Ca, Si,Mo, Zr, Ti, V, Nb, Zn, Y, W, Cu, Al, Au, Ag, Pb, B, Ge, In, Sm, andcompounds of these materials with C and B.

Similarly, catalyst materials suitable for cBN synthesis can include anycatalyst capable of promoting growth of cBN from suitable boron nitrideraw materials. Non-limiting examples of suitable catalyst materials forcBN growth include alkali metals, alkali earth metals, and compoundsthereof. Several specific examples of such catalyst materials caninclude lithium, sodium, calcium, magnesium, barium, nitrides of alkaliand alkali earth metals such as Li₃N, Ca₃N₂, Mg₃N₂, CaBN₂, and Li₃BN₂.Additionally, the catalyst material can include Al, Fe, Co, Ni, andalloys thereof. The catalyst materials under cBN synthesis can furtherinclude very minor amounts of additives which control the growth rate ofcBN crystal such as Si, Mo, Zr, Ti, Al, Pt, Pb, Sn, B, C, and compoundsof these materials with Si, B, and N.

Dimensions of the particulate catalyst layer 14 can vary considerably.However, the thickness of the layer should allow raw material such ascarbon to diffuse toward the crystalline seeds sufficient to allowcrystal growth at an interface between the crystalline seeds and thesurrounding catalyst material. In one aspect of the present invention,the raw material layer and/or particulate catalyst layer can be formedby cold pressing powder to form a coherent mass which is then slicedinto thin layers such as a disk for use in the present invention. Thepressed disks can then be stored for later use and can be easily placedin a mold as described above.

Referring now to FIG. 3, in accordance with the present invention,crystalline seeds 20 can be placed in a predetermined pattern on theparticulate catalyst layer 14. By placing crystalline seeds in a regularpredetermined pattern, growth conditions can be optimized to efficientlyuse available growth volumes, increase crystal quality, and decreasesize distribution of grown superabrasive particles. The crystallineseeds can be any suitable seed material upon which growth can occur foreither diamond or cBN. In one aspect of the present invention, thecrystalline seeds can be diamond seeds, cBN seeds, or SiC seeds. Thesynthesis of either diamond or cBN can utilize such crystalline seeds.Frequently, diamonds seeds are the preferred crystalline seeds fordiamond synthesis. Further, in some embodiments of cBN synthesis, cBNseeds can be used. Alternatively, the crystalline seeds can bemulti-grained such that a plurality of smaller crystals are bondedtogether to form each crystalline seed. Most often, when placingcrystalline seeds in the catalyst layer, the crystalline seeds arepreferably uncoated seeds, i.e. they do not include additional metal orother coatings around crystalline seed.

Typically, the crystalline seeds can have a diameter of from about 30 μmto about 500 μm, and preferably from about 55 μm to about 500 μm.However, the present invention is ideally suited to patterned placementand growth of almost any size crystalline seed. Allowing for largercrystalline seeds also reduces the growth time required to produce largesuperabrasive particles. In particular, diamond seeds suitable for usein the present invention can be larger than typical diamond seeds, i.e.from about 200 μm to about 500 μm, although the above ranges can also beeffectively used. Alternatively, the crystalline seeds can have adiameter from about 10 μm to about 50 μm, and in some cases from about20 μm. The methods of the present invention allow for extended growthtimes while also avoiding incorporation of inclusions. As a generalguideline, typically crystalline seeds can have an average diameter fromabout 0.05 to about 0.2 times the average diameter of the desired grownsuperabrasive particles. In one detailed aspect, suitable diamond seedscan be type IIa diamond and may be synthetic or natural diamond.Alternatively, synthetic cBN or SiC seeds can be used. In an additionalalternative embodiment, the crystalline seeds can be a mixture ofdifferent types of seeds, i.e. two or more of diamond seeds, cBN seeds,and SiC seeds.

Arrangement of crystalline seeds in the predetermined pattern can beaccomplished in any number of ways. In one embodiment, the crystallineseeds can be arranged in a predetermined pattern using a template toguide placement of the seeds. FIG. 1 shows a side view of a template 16which can be placed upon the particulate catalyst layer 14. For improvedconsistency and accuracy, the template can be optionally aligned usingguiding pins or the like.

Suitable templates can be formed of almost any material in which apattern of apertures can be formed. The apertures 18 can be sized toaccommodate a single crystalline seed 20 in each aperture. The aperturesare typically circular; however any other practical shape can be used.Typically, the template 16 can be formed of a metal sheet such asstainless steel, nickel, aluminum, or hard plastics. However, othermaterials such as polymeric, ceramic, or composite materials can also beused to form the template. In one aspect of the present invention, thetemplate can be prepared by forming holes which extend completelythrough the material as shown in FIGS. 1 and 3. Alternatively, the holescan be formed only partially through the material to form a divot orindentation. In this embodiment, the template can also act as a transfersheet to place the crystalline seeds on a substrate. In either case, theholes can be formed using any known method such as mechanical orchemical methods. Several examples can include laser drilling,micro-drilling, computer numerically controlled (CNC) drilling, chemicaletching, and the like. In one aspect of the present invention, thetemplate can be a sieve.

The predetermined pattern can be almost any pattern which places thecrystalline seeds at distances suitable for crystal growth. FIG. 2Aillustrates one embodiment where the predetermined pattern can be aregular grid pattern of apertures 18 in a template 16 which can be usedto place crystalline seeds at regular intervals in both the x and ydirections. Alternatively, the predetermined pattern can be a series ofoffset rows as shown in FIG. 2B. In yet another alternative embodiment,the apertures 18 can be formed such that varying concentrations ofcrystalline seeds can be arranged or even varying sizes of crystallineseeds can be placed on the particulate catalyst layer 14 (FIG. 3). Forexample, predetermined patterns having variations in the size ofapertures can be filled by first placing larger crystalline seeds tofill in larger apertures and then filling smaller apertures with smallermesh crystalline seeds.

The spacing of apertures 18 in a template 16 can vary somewhat. However,the apertures should be formed such that individual crystalline seedsare placed from 400 μm to about 1.5 mm apart. Those skilled in the artwill recognize that spacing outside this range can also be used and candepend on the size of the crystalline seeds and the desired final grownsuperabrasive sizes. It should be noted that these distances aremeasured from center to center. As additional guidance, the aperturescan be formed so as to place crystalline seeds a distance apart whichallows each seed sufficient space to receive raw material withoutcompetition from neighboring crystals. Depending on the desired finalsize of the superabrasive particles, the spacing between grownsuperabrasive particles can range from about 300 μm to about 1000 μm,although distances outside this range can also be used. Typically, thefinal diameter of the grown superabrasive particles leaves at least adistance of about 0.8 times the final diameter of the grownsuperabrasive particles between edges of nearby grown superabrasiveparticles, and preferably from about 1.2 to about 3 times the finaldiameter. For example, a spacing of from about 800 μm to about 900 μmcan be used to grow particles having a diameter of from about 425 μm toabout 600 μm (30/40 mesh). In another example, a spacing of about 650 μmcan be allowed between grown superabrasive particles having a size ofabout 45 mesh, while a spacing of about 800 μm can be allowed for largergrown particles of about 35 mesh. In yet another example, a spacing offrom about 700 μm to about 1.5 mm can be used to grow 30/40 mesh (600 to425 μg/m) grown diamond. Excessively large spacing between apertures canresult in significant amounts of wasted space and raw materials, whilean aperture spacing which places crystalline seeds too close can resultin large numbers of crystals growing together. Those skilled in the artcan make appropriate adjustments to spacing in order to compensate forshrinkage during HPHT growth.

In accordance with the present invention, a thin layer of binder can becoated over at least a portion of a surface of the growth precursorprior to placement of crystalline seeds thereon. This can help toprevent seeds from leaving their predetermined positions and furtherincreases ease of handling during manufacture. The use of an adhesivelayer can result in a predetermined pattern that is substantially freeof vacant positions or misplaced crystalline seeds with respect to thepattern of apertures. The layer of adhesive can be formed using anysuitable process such as, but not limited to, spraying, film coating,spin coating, extrusion coating, and the like. Spraying is typicallyconvenient and effective in producing a thin and uniform layer ofadhesive.

Suitable binders can include, but are not limited to, organic binderssuch as acrylic adhesives, wax, polyethylene glycol, polyvinyl alcohol,paraffin, naphthalene, polyvinyl butyral, phenolic resin, wax emulsions,and mixtures thereof. Currently preferred organic binders includeacrylic adhesives, polyethylene glycol, and polyvinyl alcohol. In onespecific example, an acrylic adhesive spray available from 3M Companycan be diluted with a solvent such as acetone and then sprayed on thegrowth precursor.

The layer of adhesive thus prepared can be of almost any functionalthickness. However, as a general guideline the layer of adhesive canhave a thickness from about 1 μm to about 50 μm. The thickness of thelayer of adhesive can typically correspond to that which is sufficientto hold the crystalline seeds in place. Excessive adhesive can beundesirable. As mentioned herein, it is often desirable to minimizeorganic content in the growth precursor placed in a HPHT apparatus.Specifically, such materials can interfere with particle growth and canbe optionally removed during a subsequent dewaxing step in order todrive off organic materials. The dewaxing step can preferably beperformed using a growth precursor which is substantially complete suchthat all of the crystalline seeds are secured within the growthprecursor. Securing can be accomplished by stacking adjacent layers ordisks of raw material, catalyst material, and/or inert material adjacentthe patterned placement of seeds. In this way, removal of the organicbinders will not disturb the predetermined pattern of crystalline seeds.

As shown in FIG. 3, crystalline seeds 20 can be placed into theapertures 18 of the template 16. An excess of crystalline seeds can bespread over the template surface such that each of the apertures isfilled with a single crystalline seed. The excess crystalline seeds canbe swept away or otherwise removed leaving particles placed on theparticulate catalyst layer 14 as shown in FIG. 3. The template can havea thickness which varies depending on the size of the crystalline seedsand the process. Typically, the thickness of the template can be fromabout 0.6 to about 1.1 times the diameter of the crystalline seeds. Oncethe crystalline seeds are placed in the apertures of the template, thetemplate can then be removed leaving the crystalline seeds in apredetermined pattern on the particulate catalyst layer. The templatecan then be reused or discarded depending on its condition. As shown inFIG. 4, a metal plate 22 or other hard surface can be used to press thecrystalline seeds 20 at least partially into the particulate catalystlayer 14. Optionally, if the template has a thickness which is less thanthe diameter of the crystalline seeds, the template can be left in placeduring pressing in order to control the distance the crystalline seedsare embedded into the catalyst layer and then removed subsequently. Inone embodiment of the present invention, the crystalline seeds 20 can bepressed into the catalyst layer such that from about half to about theentire particle is buried into the catalyst layer. In one aspect,crystalline seeds can be pressed completely into the catalyst layer suchthat each crystalline seed is substantially surrounded by catalystmaterial.

In accordance with the present invention, any exposed portions of thecrystalline seeds 20 can be covered with additional metal catalystmaterial such that the catalyst material substantially surrounds eachcrystalline seed to form a growth precursor 24, as shown in FIG. 5.Typically, in this embodiment of the present invention, the thickness ofthe initial particulate catalyst layer 14 (FIGS. 1, 3 and 4) can be fromabout 0.5 to about 0.9 times the diameter of the crystalline seeds, andpreferably about 0.7. The exposed crystalline seeds can be covered byplacing additional catalyst material on the exposed crystalline seedsand then optionally pressing to reduce porosity to less than about 33%to produce the growth precursor 24 shown in FIG. 5.

In one alternative embodiment, the exposed portions of the crystallineseeds can be covered with a metal catalyst plate or foil, although apowder metal catalyst is preferred due to some inherentnon-homogeneities in solid plates. The particulate catalyst layer 14preferably has a thickness which is sufficient to initially completelysurround each crystalline seed. During crystal growth, the metalcatalyst material continues to wet the surface of the crystalline seed.Therefore, the thickness of the particulate catalyst layer need not begreater than the diameter of the grown superabrasive particles.

During diamond synthesis, the graphite to metal catalyst ratio candetermine the availability of raw materials for formation of diamond.Typically, the graphite to metal catalyst ratio can range from about 0.5to about 2.0 by weight, and preferably from about 0.7 to about 1.5. Inone aspect, the catalyst metal can be provided in an amount sufficientto form a layer of molten catalyst metal during growth conditions havinga thickness of from about 20% to about 60% of the diameter of thediamond during growth.

Referring now to FIG. 6, additional raw material layers 12 andparticulate catalyst layers 14 can be formed to improve efficient use ofa high pressure high temperature (HPHT) apparatus cell volume. Thethickness of each layer can depend on the diameter of the crystallineseeds 20 and the projected diameter of the final grown superabrasiveparticles. Additionally, the thickness of the layers will also affectthe distance between crystalline seeds in nearby catalyst layers. Thepredetermined pattern in each particulate catalyst layer can beconfigured such that upon assembling layers as in FIG. 6, the assemblyalso exhibits a predetermined pattern across the thickness of the growthprecursor 24. The pattern shown in FIG. 6 is an offset pattern; howeverany suitable arrangement can be used, as long as grown crystals do notimpinge on neighboring grown crystals. Typically, the particulatecatalyst layers can have a thickness of from about 50 μm to about 500μm, while the raw material layer can have a thickness of from about 70μm to about 1 mm. Those skilled in the art will recognize thatthicknesses and configurations outside of the identified ranges can alsobe used.

Typical HPHT reaction cells can have a reaction volume of from about 15cm³ to about 100 cm³. Therefore, it is often practical to include alarge number of layers in the growth precursor in order to fully utilizeavailable reaction volume for crystal growth. In one aspect of thepresent invention, the growth precursor can have from about 3 to about50 layers. In addition, formation of each layer and placement ofcrystalline seeds can be preceded or followed by a pressing step inorder to reduce porosity and improve the cohesiveness of the growthprecursor. Thus, in one preferred embodiment, each layer can be pressedprior to pressing the entire multi-layer growth precursor. Pressing canbe preferably accomplished by cold isostatic pressing although otherpressing techniques can also be used.

Placement of Crystalline Seeds in a Predetermined Pattern

As mentioned above, the crystalline seeds can be placed in apredetermined pattern using any number of methods. Those of ordinaryskill in the art will recognize a variety of ways for locating particlesat desired locations on a surface or substrate. A number of techniqueshave been developed for placing superabrasive particles in a pattern forproduction of abrasive tools. For example, U.S. Pat. Nos. 2,876,086;4,680,199; 4,925,457; 5,380,390; and 6,286,498, each of which isincorporated by reference, disclose methods of placing superabrasiveparticles in a pattern for forming various abrasive tools.

An alternative method for placing crystalline seeds in a predeterminedpattern can include providing a transfer sheet having an adhesive layerthereon. The transfer sheet can be any material which is self-supportingand capable of transporting crystalline seeds to a catalyst layer. Atemplate, such as those discussed above, can then be placed upon theadhesive layer. For example, a template can be placed upon a transfersheet such as an adhesive tape or other adhesive material. Preferablythe adhesive layer is sufficiently tacky to hold the crystalline seedswhich contact the adhesive while also allowing for easy removal of thetemplate. Non-limiting examples of moderately tacky adhesives suitablefor use with a transfer sheet include acrylic adhesives and polymericadhesive microspheres, e.g., such as those used in POST-IT (trademark of3M Company) notes. Alternatively, the template can have a surface coatedwith a smooth and/or non-stick material such as TEFLON or the like, inorder to facilitate removal of the template. The apertures of thetemplate can then be filled with crystalline seeds as discussed above.After removing the template, the transfer sheet having patternedplacement of crystalline seeds can be contacted with the growthprecursor having a layer of adhesive thereon. The transfer sheet can beoriented between the crystalline seeds and the catalyst layer. Dependingon the material used, the transfer sheet may decompose during theinitial stages of HPHT.

Alternatively, the transfer sheet can be oriented such that thecrystalline seeds are between the transfer sheet and the particulatecatalyst layer. The transfer sheet can then be removed or left in place.In order to facilitate removal of the transfer sheet without disturbingthe crystalline seeds, the particles can be pressed partially into theparticulate catalyst layer. Of course, the composition of the adhesivelayer can also be adjusted to reduce the tackiness of the adhesive. As apractical matter, it can be desirable to utilize an adhesive on thegrowth precursor which has a higher tackiness than the adhesive of thetransfer sheet such that transfer of the particles from the transfersheet to the growth precursor is made easier.

Alternatively, the transfer sheet can be a metal catalyst layer such asa foil or disk formed of metal catalyst material used in the particulatecatalyst layer. The metal catalyst foil layer can remain in place tohelp surround the crystalline seeds with metal catalyst material. Insuch an embodiment, it can be desirable to partially embed thecrystalline seeds into the foil in order to avoid the use of organicbinders which may adversely affect crystal growth. Regardless of thespecific transfer sheet process used, the crystalline seeds can then beat least partially pressed into the particulate catalyst layer.

In yet another alternative embodiment of the present invention, thecrystalline seeds can be placed in a predetermined pattern using vacuumchuck. Specifically, a vacuum chuck can be formed having a pattern ofapertures therein. The apertures can be configured to hold a singlecrystalline seed such that pulling a vacuum through the aperturesengages a single crystalline seed in each aperture. Thus, the aperturescan have an initial portion sized slightly smaller than the crystallineseed and which are connected to a vacuum source. In practice, a vacuumcan be pulled through the apertures and the chuck can then be placed ina supply of crystalline seeds. The chuck can then be oriented over theparticulate catalyst layer, or optionally a transfer sheet and thevacuum can be reduced sufficient to release the crystalline seeds thusarranging the crystalline seeds in a predetermined pattern correspondingto the pattern of apertures in the chuck. The crystalline seeds can thenbe pressed at least partially into the catalyst layer in a similarmanner as discussed above.

Alternatively, the crystalline seeds can be placed in a predeterminedpattern on the raw material layer, rather than the catalyst layer, usingany of the above-described methods, i.e. template, sieve, transfersheet, and the like. It will be understood that any of the methodsdescribed above for placement of the crystalline seeds in apredetermined pattern can also be used on the raw material layer.Typically, diamond seeds can be coated with a catalyst metal prior toplacement in the raw material layer in order to prevent direct contactof the diamond seeds with raw carbon or graphite. Coating of diamondparticles is known in the industry and can be accomplished using anynumber of available methods. Typically, diamond particles can be coatedby a catalyst metal such as Fe, Ni, Co, and alloys thereof. Catalystcoatings of nickel and nickel alloys are particularly preferred. Themetal coating can help provide a molten catalyst layer surrounding thediamond seeds during HPHT growth and prevent direct contact withgraphite or other carbon raw materials. The coating can have a thicknesswhich varies from about 2 μm to about 50 μm, although thickness abovethis range can also be used.

In yet another alternative embodiment, the crystalline seeds can beplaced in a predetermined pattern by forming polycrystalline seeds froma slurry using a method such as screen printing, other lithographictechniques, or the like. Thus, the crystalline seeds can bepolycrystalline or monocrystalline. In accordance with this embodiment,the polycrystalline seeds can be prepared by forming a slurry of diamondparticles, catalyst metal powder, an organic binder, and an optionalsolvent. The slurry can be formed into a plurality of polycrystallineseed precursors and then removing the organic binder and optionalsolvent to form polycrystalline seeds.

The diamond particles can be almost any functional size. As a generalguideline, sizes from about 1 μm to about 15 μm can be useful, andtypically from about 2 μm to about 4 μm. The final size of thepolycrystalline seed can be about the same as crystalline seeds hereindiscussed; however, in many cases the seeds can be less than about 10μm. Additionally, the catalyst metal powder can comprise catalystmaterial as discussed above in connection with other embodiments, orembodiments which can be used in conjunction with polycrystalline seeds.Typically, the catalyst can comprise from about 5 vol % to about 50 vol% of the polycrystalline seed.

Non-limiting examples of suitable organic binders can includepolyethylene glycol (PEG), polyvinyl alcohol, methyl propyl cellulose,carboxy methyl cellulose, hydroxy ethyl cellulose, methyl ethylcellulose, polyvinyl butyral, acrylic resin, coal tar pitch, long chainfatty materials, sugars, starches, alginates, polystyrene, celluloseacetate, phenolic resins, and mixtures thereof. An optional solvent canbe included to adjust the viscosity of the slurry to accommodate aparticular printing technique. Suitable solvents can include, but arenot limited to, acetone, ethanol, isopropanol, glycols, methanol,trichlorethylene, toluene, and mixtures thereof.

For example, the slurry can be printed onto a surface, e.g., of thegrowth precursor or particulate growth layer, to form polycrystallineseed precursors. The organic binder and optional solvent can be removedin a drying and/or dewaxing step. For example, a first heating step canbe used to remove any solvent, e.g., about 100° C. for about 4 hours,and a second dewaxing step can be used to remove the organic binder,e.g., heating at 600° C. for about 2 hours (usually under a vacuum). Thefinal polycrystalline seeds typically include diamond particles andcatalyst metal. Optimal results can be achieved when the final grownsuperabrasive particles have a size greater than about 10 times that ofthe polycrystalline seed.

In accordance with the present invention, polycrystalline seeds havebeen found to produce final grown superabrasive particles having amonocrystalline structure. It appears that the growth conditions of thepresent invention allow the polycrystalline seeds to merge and form asubstantially single crystal. Superabrasive particles formed in thismanner tend to allow for microfracturing of the particle during abrasiveapplications. Typical superabrasive particles tend to either become dullor macrofracture making the remaining particle useless. However,microfractures allow the particle to periodically expose new sharp edgesand retain the bulk of the particle for extended useful life.

Mixture Growth Precursors

In yet another alternative embodiment of the present invention, a methodfor controlling nucleation sites during superabrasive particle synthesiscan include forming a particulate crystal growth layer. Generally, agrowth precursor can be formed and then heating sufficient to growsuperabrasive particles having a preselected morphology. The growthprecursor can be formed to include a substantially homogeneous mixtureof raw material and catalyst material. Further, the growth precursor canhave crystalline seeds in a predetermined pattern at least partiallytherein. It will be understood that the principles and considerationsdescribed above with respect to layered growth precursors can also beused in connection with growth precursors comprising a substantiallyhomogeneous mixture of raw material and catalyst material.

Referring now to FIG. 7, the particulate crystal growth layer 15 can bea substantially homogeneous mixture of particulate raw material andparticulate catalyst material. Crystalline seeds 20 can be placed in apredetermined pattern at least partially in the particulate crystalgrowth layer to form a growth precursor 24 using the same methodsdiscussed above. Additionally, the growth precursor can include a singlelayer or multiple layers as shown in FIG. 7. The materials, ranges,patterned placement methods, and other aspects discussed above can alsobe applied to the particulate crystal growth layers comprising a mixtureof raw material and catalyst material. In one aspect, the growthprecursor can consist essentially of raw material, catalyst material,and crystalline seeds.

As mentioned earlier, an uncoated diamond seed substantially surroundedby graphite can be undesirable. However, surrounding the diamond seedswith a mixture of carbon source material and catalyst allows thecatalyst powder to wet the surface of the diamond seeds and coat thesurface thereof. This wetting effect is at least partially the result ofcarbide bonds forming between the diamond and the solvent metal. Diamondmay initially dissolve because the catalyst metal is under-saturatedwith carbon; however, once the catalyst metal is melted, the carbonbegins to diffuse into the molten catalyst. The dissolved or suspendedcarbon will soon adhere to the surface of the diamond seed and allow theseed to grow.

In one currently preferred embodiment, the diamond seeds can be coatedwith a catalyst material. In some embodiments, the coating can consistessentially of a catalyst material. Typically, the coating can be acatalyst material having a melting temperature within about 5° C. of themelting temperature of the catalyst material used in the particulatecatalyst layer. This helps to avoid the metals from melting atsignificantly different times thus reducing the quality of the finalgrown diamond. Diamond seeds can be coated with a catalyst materialusing any known technique. Coating of diamond particles has historicallyproven difficult, since most catalyst metals cannot be easily coated ondiamond to the required thickness, involve significant expense, and/orleave undesirable organic residual materials. Several examples ofcoating technologies include, without limitation, electroplating,chemical (e.g., electroless) deposition, physical vapor deposition(e.g., sputtering), chemical vapor deposition, fused salt coating, andthe like.

In one embodiment, the catalyst metal can be nickel; however, othercatalyst metals can be also suitable. FIGS. 8A and 8B show aphotomicrograph of nickel coated diamond particles in accordance withone embodiment of the present invention. Nickel coatings typically havea highly irregular surface topography characterized by small protrusionsor spikes. This irregular topography has the added benefit of increasingsurface area contact between the catalyst coating and catalyst metal inthe mixture of the growth precursor. In this way, additional catalystmaterial can easily diffuse into the catalyst coating during crystalgrowth in order to maintain a coating of sufficient thickness to preventdirect contact between the diamond and raw material. As diamond growthoccurs, the diamond surface area increases, thus having the tendency todecrease the catalyst coating thickness. However, in accordance with thepresent invention, the catalyst coating thickness can be maintained byadjusting the amount of catalyst material in the growth precursor. Thecatalyst coating can have a thickness which is sufficient to preventsubstantial direct contact between the diamond and raw material.Typically, the catalyst coating can have thickness which is about 0.5 toabout 1.3 times the diameter of the particle. For example, a diamondseed having a diameter of 40 μm can be coated to a final diameter ofabout 100 μm. Thus, the coating thickness in this case is about 30 μm.The larger crystalline seed can also improve the accuracy and speed ofplacing the seeds in a predetermined pattern. As a practical matterparticles smaller than about 50 μm can be difficult to reliably placeusing a template.

In still another aspect of the present invention, the crystalline seedscan be arranged on a metal catalyst layer such as a foil or disk to forma predetermined pattern of crystalline seeds. The crystalline seeds canbe placed on the metal layer in a manner similar to that describedabove. A substantially homogeneous mixture of catalyst material and rawmaterial can be formed around the crystalline seeds and thenconsolidated to reduce porosity of the growth precursor. Additionallayers can be formed by then placing another metal catalyst layer on thegrowth precursor and repeating the above steps to produce amulti-layered growth precursor having almost any number of layers. Themetal catalyst layer can comprise any catalyst material suitable forgrowth of the superabrasive particle. Typically, the metal catalystlayer can have a thickness from about 20 μm to about 0.10 mm, althoughany functional thickness can be used. Generally, the number of layers ina multi-layered precursor can vary depending on the HPHT apparatus to beused. Typically, the height of the precursor is about 80% of thediameter, although this can vary somewhat.

The metal catalyst layer can provide a substantially flat surface whichhas improved mechanical support for the growth precursor. Additionally,during growth of the superabrasive particles, the layer can provide aninitial source of catalyst material for maintenance of the catalystcoating around the growing superabrasive particle. As the superabrasiveparticle continues to grow, the primary source of additional catalystmaterial can then be the mixture of catalyst and raw material.

In another optional aspect of the present invention, the growthprecursor can be coated along exterior surfaces with a metal coating.Suitable metal materials can include Fe, Ni, Co, and alloys thereof. Theexterior metal coating helps to prevent the precursor from adhering orbonding to reaction cell walls of the HPHT apparatus under growthconditions. The coating thickness can be any thickness which issufficient to provide the above benefit; however, typical thicknessescan range from about 50 μm to about 300 μm. In yet another optionalaspect, a layer of separator material can be included adjacent thegrowth precursor in a reaction cell volume of the HPHT apparatus. Alayer of NaCl can typically be used as the separator material; howeverother materials can also be used.

The growth precursor can then be subjected to a temperature and pressurein which diamond or cBN is thermodynamically stable. As the temperatureand pressure are increased to sufficient growth conditions, raw materialsuch as carbon migrates toward the crystalline seeds. The catalystmaterial surrounding individual crystalline seeds form a catalyst layersubstantially surrounding each seed, assuming sufficient catalystmaterial is present to form such a coating. The catalyst coatingfacilitates formation of diamond or cBN at the surface of thecrystalline seeds. The growth conditions are maintained for apredetermined period of time to achieve a specific size of grownsuperabrasive particle.

Advantageously, the methods of the present invention enable a highdegree of control over the growth conditions of each superabrasiveparticle. The highly regular placement of seeds and the substantiallyhomogeneous growth precursor compositions allow for precise control oftemperature throughout the growth precursor. As a result, the growth ofindividual superabrasive particles can be nearly uniform throughout thegrowth precursor. The final collection of superabrasive particles aretherefore highly uniform in shape, size, and quality. Typically, thecollection of grown superabrasive particles can have a narrow sizedistribution characterized by a standard deviation of less than about0.2 of the average size of unsorted and unsized particles, andpreferably less than about 0.1 and most preferably less than about 0.05of the average size. For example, a narrow size distribution having astandard deviation (2 a) within about 0.05 of an average sizecorresponds to about 95% of the particles falling within about 5% of theaverage. In many cases, the size distribution can have a standarddeviation (3 a) from the average size of less than about 0.2 of theaverage size and in many cases less than about 0.1, e.g., a singleassembly of grown particles having an average size of about 100 μm willhave substantially no particles outside the range of about 90 μm toabout 110 μm.

The final grown superabrasive particles can be recovered from the growthprecursor using any number of known methods. For example, any remainingmetal matrix can be removed by dissolving in warm aqua regia andremaining graphite can be removed in hot sulfuric acid. The recoveredsuperabrasive particles can then be further cleaned and/or prepared forcommercial use.

Diamond Growth Considerations

In accordance with the present invention, growth precursors can includediamond seeds located at controlled locations such that each seed issubjected to substantially identical growing environments. In this way,each seed can grow to substantially similar sizes and quality. Thistechnology allows for custom dialing of the size and quality so nearlythe entire output is uniform for a particular application or customer.Due to this increase in uniformity of growth conditions, a number ofadvantages can be realized. For example, the crystal morphology can becontrolled to produce superabrasive particles having a preselectedmorphology, e.g., octahedral, cubo-octahedral, etc. The followingdiscussion provides guidance in obtaining specific results using themethods of the present invention, without being bound by any particulartheory presented.

Diamond growth can be accomplished by providing dissolved carbon atomsor by puckering layers of graphite which add to an existing diamondcrystal face. FIG. 9A shows an octahedral (111) face of diamond inprogress of growth. As shown in FIG. 9B the carbon atoms contained inthis layer contain one unbonded, or dangling, electron. The octahedralface of diamond can be dominantly formed by puckering of graphitelayers, shown in FIG. 9C. If nano-sized flakes of graphite(graphite-like carbon or GLC) are present, these flakes can be readilyrearranged to form rhombohedral graphite as shown in FIG. 10A. Therhombohedral graphite can be readily puckered to form diamond-likecarbon (DLC) as shown in FIG. 10B. The diamond-like carbon can then addto the octahedral (111) face of diamond as illustrated in FIG. 10C.Additional details on such a method of forming rhomohedral graphite maybe found in Applicant's copending application, U.S. patent applicationSer. No. 10/900,037, filed Jul. 24, 2004, which is incorporated hereinby reference.

Similarly, the cubic (100) face of diamond is shown in FIG. 11A. It isinteresting to note that these atomic scale atomic arrangements affectthe macroscale crystalline structure, i.e. cubic versus octahedral facesof diamond particles. The carbon atoms on the cubic face of diamondcontain atoms having two dangling electrons as shown in FIG. 11B. Thus,carbon atoms can be easily attached to the cubic face such that growthof diamond occurs perpendicular to this face, as shown by FIG. 11C.

Referring now to FIG. 12A, diamond growth mechanisms will be discussedin more detail. FIG. 12A illustrates a growing diamond particle 30surrounded by a catalyst material 32. A portion of a cubic (100) face 36of the diamond particle and a portion of an octahedral (111) face 38 arealso shown. The catalyst material envelope 32 surrounding the diamondparticle is also in contact with a raw material 34 which diffusesthrough the catalyst envelope. FIG. 12B shows a portion of the cubicface 36 under growth conditions which favor growth on this plane.Specifically, at relatively high temperatures, graphite will dissolve toform atomic carbon solutes. These carbon atoms tend to deposit asdiamond on the cubic face of diamond. Growth of the cubic faceperpendicular to the face will result in the cubic face becoming smallersuch that the growing diamond will become more and more octahedral.

Conversely, as shown in FIG. 12C, if the temperature is relatively low,graphite will disintegrate in the molten catalyst to form graphite-likecarbon (GLC) that will be puckered under catalytic action to becomediamond-like carbon (DLC). The DLC will add to the octahedral (111) faceof diamond. As a result, growth perpendicular to the (111) face willshrink this face and make the diamond crystal more and more cubic. Forexample, FIG. 13A illustrates diamond growth at low temperature suchthat DLC preferentially deposits on the octahedral (111) face so thecrystal will become more cubic. Conversely, a higher temperature willfavor carbon atoms depositing on the cubic face so the diamond crystalwill become more octahedral, as shown in FIG. 13B. According to anembodiment of the present invention, the ability to achieve apreselected morphology is greatly increased. For example, in some cases,the grown diamonds from an unsorted single run can have greater than70%, preferably greater than about 85%, and most preferably greater thanabout 90% of the grown particles being a desired morphology, e.g.,cubic, octahedral, or cubo-octahedral.

The diamond morphology is determined by the relative growth rateperpendicular to (100) and (111) faces. In FIG. 14, the fastestdirection of diamond growth (the largest size of the crystal) ismeasured by α=√3V(111)/V(100), where V is the growth rate in a directionperpendicular to the identified face. FIG. 15 shows a photomicrograph ofcommon premium quality saw grits having euhedral crystal morphology.These premium saw grits are typically cubo-octahedral as can be seen inthe figure. The octahedral (111) face has the highest packing density ofcarbon atoms, relative to other diamond faces. As a result, theseparation of octahedral faces from one another is farther such thatfailures of diamond particles tend to occur along this cleavage plane.As carbon atoms are added to the (111) face, they tend to spread alongthe face rather than to spread across the plane. On the other hand, ifDLC is preferentially deposited, the octahedral plane will growperpendicular to the (111) face. Additionally, octahedral diamond has amore acute angle than other shapes of diamond. Thus, octahedral diamondsare highly desirable for making single point cutters as well as wiredrawing dies.

The temperature effect on diamond morphology allows for adjustment ofthe temperature based on the diamond itself to carefully control theresulting morphology. Thus, if diamond is too cubic, temperature can beincreased by adding electrical heating power to make it more octahedral.On the other hand, lower electrical power can make diamond more cubic.The methods and growth precursors of the present invention allow forincreased control and manipulation of these subtle temperature effectson crystal morphology. For example, in order to achieve dominantlyoctahedral diamonds a temperature from about 1305° C. to about 1320° C.can be used. Similarly, a temperature from about 1250° C. to about 1310°C. can be useful for obtaining cubic or cubo-octahedral diamonds.However, these temperature ranges are merely general guidelines as theactual values can vary depending on the specific catalyst material andraw material used. In accordance with the present invention, thetemperature can be controlled to within about 10° C. throughout thegrowth precursor during crystal growth, typically within about 5° C. andin some cases within about 2° C.

Thus, in accordance with the present invention, synthetic octahedraldiamonds can be produced in large quantities having very few inclusions.Further, the synthetic octahedral diamond of the present invention canbe formed in relatively large sizes. For example, sizes greater thanabout 1 μm and often greater than about 10 μm can be easily realized.Generally, useful synthetic octahedral diamond can have a size fromabout 1 μm to about 10 mm, with sizes from about 20 μm to about 5 mmbeing preferred.

Referring now to FIG. 16, a graph shows various guidelines and aspectsfor consideration when using the methods of the present invention.During diamond growth, if the diamond seed is in contact with rawmaterial, diamond is not formed so either graphite or metal will betrapped as inclusions to form highly included diamond. Consequently, itis important that diamond be enveloped in a molten layer of catalyst toallow uninterrupted growth of diamond. For example, diamond surface areais proportional to the square of the diamond size. Additionally, thesupply of catalyst is proportional to the size of the growing diamond.As such, the thickness of the catalyst coating can gradually decrease asthe diamond becomes larger. Thus, the substantially homogeneous mixturesof the present invention can provide a relatively uniform supply ofadditional catalyst material which can maintain a sufficiently thickcatalyst coating around the growing diamond. Thus, both raw material andcatalyst material tend to diffuse toward the growing diamond.Maintaining a substantially continuous catalyst envelope around eachgrowing crystal helps to significantly reduce the number of inclusionsin the grown diamonds.

FIG. 17 illustrates the growth of diamond seeds 20 in the presence ofthe surrounding catalyst material 26 to form a grown diamond 28. Directcontact of diamond seeds directly with the carbon source material cancause an undesirable number of inclusions. Typical growth conditions canvary somewhat; however, the temperature can be from about 1200° C. toabout 1400° C. and the pressure can be from about 4 to about 7 GPa. Theappropriate temperature can depend on the catalyst material chosen. As ageneral guideline, the temperature can be from about 10° C. to about200° C. above a melting point of the catalyst. Growth time can typicallybe from about 5 minutes to about 2 hours. The patterned placement ofcrystalline seeds in the present invention also allows for relativelylarge variations in process conditions. For example, temperature andpressure can deviate from about 1% to about 10%, and in some cases canbe from about 3% to about 5%. This allows for less strict control ofprocess conditions than conventional methods, while also maintaining thequality of grown superabrasive particles. Typically, crystal growth inaccordance with the present invention can be substantially epitaxialgrowth such that high quality superabrasive particles having high impactstrength are produced. Further, the methods of the present invention canbe fully automated and reduce the need for manual evaluation andprocessing.

In addition to the above considerations, the inclusion level can befurther reduced by removing contaminants (e.g. oxygen on the metal,moisture in the graphite) from the reaction cells. One effective way toremove such contaminants is to subject the growth precursor, catalystmaterials, and/or raw materials to a high vacuum (e.g. 10⁻¹ Pa) at hightemperature (e.g. 1100° C.) for an extended period of time (e.g. 2hours). During this heat treatment, hydrogen can be used to purge thematerials to further remove oxygen. Nitrogen can also be used to purgeto make the diamond more rich in yellow color. Once these contaminantsare substantially removed, the grown diamond can be highly transparentwith a minimal level of inclusions. Diamond can also be back-convertedto amorphous carbon (an intermediate step toward graphite) by any metalcatalyst that is trapped inside of diamond crystal. Typically, thisback-conversion can start at temperatures above 700° C. As soon asamorphous carbon is formed around the catalyst inclusion, the resultingvolume expansion can cause diamond to microcrack. As a result, impactstrength of the diamond can decrease. Thus, diamond with lower inclusionlevels can survive better at high temperatures of hot pressing andimpact cutting. Diamonds grown in accordance with the present inventionpossess high impact strength and high thermal stability such that theycan be processed at high temperature (e.g. 1000° C.) to make diamondtools and used for aggressive cutting applications. As a generalguideline, if molten metal surrounds the seeds from the beginning of thegrowth process, diamond seed of about 20 microns will tend to dissolvesuch that the control of nucleation may be lost. On the other hand, ifthe uncoated seeds are larger than about 50 microns, then a metalcatalyst coating can be preferred. Otherwise, graphite may be in contactwith the diamond seed before molten catalyst can flow to surround theseed. Without the coating of molten catalyst, graphite can be trapped asinclusions, along with some metal.

In one detailed aspect of the present invention, the crystalline seedcan be from about 10% to about 30% of the desired grown diamond particlesize. Depending on the growth conditions and the size of the crystallineseed, the grown superabrasive particles can have a particle size fromabout 100 μm to about 2 mm. Most common superabrasive particles sizescan range from about 18 mesh to about 60 mesh. Even larger superabrasiveparticles can be grown if larger crystalline seeds are used. Typically,grown superabrasive particles useful in many abrasive and cuttingapplications can have a particle size from about 210 μm to about 1 mm.One advantage of the present invention is the uniformity of grownsuperabrasive particle sizes. The predetermined pattern and orientationof layers allows for substantially uniform nucleation and growth ofdiamond and cBN. Therefore, the grown superabrasive particles of thepresent invention have a very narrow size distribution and improvedquality when compared to particles grown from randomly nucleated andseeded precursors. For example, the size distributions using the presentinvention are typically less than half the standard deviation ofconventional random seeded methods. Typically, the grown superabrasiveparticles of the present invention also have inclusion levels which aretypically not noticeable under unaided visual inspection. Typically,yields of from about 30% to about 90% conversion of carbon to diamondcan be expected when using the present invention. Further, the percentof high quality diamond can range from 50% to about 90%, with over 70%being a typical yield. In some embodiments of the present invention, theyield of high quality diamonds can range from about 2 carat/cm³ to about5 carat/cm³, and preferably from about 3.5 carat/cm³ to about 4.5carat/cm³. FIG. 18 shows an assembly of grown diamond particles inaccordance with the present invention. In FIG. 18, the diamond particlesare substantially uniform in size and exhibit uniform euhedral crystalshapes. In this example, the diamond separation was predetermined at 0.9mm.

EXAMPLES

The following examples illustrate exemplary embodiments of theinvention. However, it is to be understood that the following is onlyexemplary or illustrative of the application of the principles of thepresent invention. Numerous modifications and alternative compositions,methods, and systems may be devised by those skilled in the art withoutdeparting from the spirit and scope of the present invention. Theappended claims are intended to cover such modifications andarrangements. Thus, while the present invention has been described abovewith particularity, the following examples provide further detail inconnection with what is presently deemed to be practical embodiments ofthe invention.

Example 1

A circular mold having a diameter of 28 mm was filled with powderednatural graphite having an average size of about 20 μm, low resistivityof about 5 μΩ-cm, and a degree of graphitization of 0.8. The graphitewas purified to be substantially free of oil, organic binders, ash, orother non-carbon materials. The graphite was cold pressed at 150 MPa toform a particulate compact disk having a thickness of 0.7 mm and adensity of 2 g/cm³ (12% porosity). High purity INVAR (Fe-35Ni with amesh size of less than 40 μm) was placed on top of the graphite layerand cold pressed at 300 MPa to form a particulate catalyst layer havinga thickness of 0.2 mm and a density of 6/cm³ (about 20% porosity). Athin layer of adhesive was sprayed onto the particulate catalyst layer.A template similar to that shown in FIG. 2B, having apertures spaced 0.8mm apart (center-to-center) and apertures 130 μm in diameter was placedon the catalyst layer. The template was covered in uncoated diamondseeds having a mesh size of 120/140 (about 115 μm in diameter) such thatthe apertures were filled. The excess diamond seeds were then collectedfor reuse. The template was removed and a metal plate was used to pressthe diamond seeds into the catalyst layer such that each of the diamondseeds was about two-thirds surrounded by catalyst material.Subsequently, additional INVAR was layered over the diamond seeds. Theadditional catalyst material was cold pressed at 150 MPa such that theentire catalyst layer had a thickness of 0.3 mm. Seven additional layersof graphite and catalyst material were formed to produce the diamondgrowth precursor. Each layer was dewaxed under vacuum at about 800° C.to about 1100° C. for two hours to remove the adhesive and other organicmatter. Exterior surfaces of the diamond growth precursor were thencoated with a 200 μm layer of iron. The diamond growth precursor wasthen placed in a belt apparatus. The precursor was then subjected to apressure of about 5.2 GPa and then heated to a temperature of about1260° C. for about one hour. The layered grown diamond assembly was thencooled and removed from the belt apparatus. The assembly was partiallycrushed to reveal grown diamonds which were substantially uniform insize and were yellow in color. The average mesh size of the growndiamonds was 30/40. Further, the grown diamonds exhibited superiorhardness, superior transparency with fully grown crystallographic faces,and very few viewable inclusions.

Example 2

A circular mold having a diameter of 28 mm was filled with powderednatural graphite having an average size of about 20 μm, low resistivityof about 5 μΩ-cm, and a degree of graphitization of 0.8. The graphitewas purified to be substantially free of oil, organic binders, ash, orother non-carbon materials. The graphite was mixed with high purityINVAR (Fe-35Ni with a mesh size of less than 40 μm). The weight ratio ofgraphite to metal catalyst was 1:1.5. The mixture was then cold pressedat 250 MPa to form a particulate compact disk having a thickness of 0.7mm and a density of 2 g/cm³ (12% porosity). The particulate compact diskwas coated with a thin layer of adhesive. A template similar to thatshown in FIG. 2B, having apertures spaced 0.8 mm apart(center-to-center) and apertures 130 μm in diameter was placed on thecompact disk. The template was covered in uncoated diamond seeds havinga mesh size of 120/140 (about 115 μm in diameter) such that theapertures were filled. The excess diamond seeds were then collected forreuse. The template was removed and a metal plate was used to press thediamond seeds into the compact disk such that each of the diamond seedswas about two-thirds surrounded by material. Subsequently, additionalgraphite and INVAR powders were layered over the diamond seeds. Theadditional powdered material was cold pressed at 250 MPa such that theentire layer had a thickness of 0.9 mm. Seven additional layers ofgraphite and catalyst material each having a pattern of diamond seedswere formed to produce the diamond growth precursor. Exterior surfacesof the diamond growth precursor were then coated with a 200 μm layer ofiron. The diamond growth precursor was then placed in a belt apparatus.The precursor was subjected to a pressure of about 5.2 GPa and thenheated to a temperature of about 1260° C. for about 50 minutes. Thelayered grown diamond assembly was then cooled and removed from the beltapparatus. The assembly was partially crushed to reveal grown diamondswhich were substantially uniform. The average mesh size of the growndiamonds was 30/40. Further, the grown diamonds exhibited superiorhardness, superior transparency with fully grown crystallographic faces,and very few viewable inclusions.

Example 3

Graphite disks were prepared by pressing natural graphite powder havinga grain size of about 20 microns into disks 37 mm in diameter and 0.8 mmin thickness at about 400 MPa. The porosity of the resulting graphitedisks was about 15%. Ni coated diamond seeds (precoated diameter ofabout 65-75 microns) having a coated diameter of about 105-125 micronswere planted into the graphite disks in a grid pattern having a pitch ofabout 0.8 mm to form seeded graphite disks. The seeded graphite diskswere alternated with INVAR (Fe65-Ni35) disks and loaded into a steelcontainer to make a final growth cell of 38.8 mm in diameter and 30 mmin height. One hundred of these growth cells were pressed in a 2500 toncubic press with a ram size of 600 mm to attain a pressure of about 5.2GPa and temperature of about 1250° C. The pressure and temperature weremaintained for 50 minutes and then the pressure was reduced and thetemperature gradually decreased. The pressed growth cells were brokenapart to reveal diamonds having 30/40 mesh with good quality andsubstantially no visible defects. Most of the grown diamonds were grownfrom the original seeds and appeared in distinct grid patternscorresponding to the original seeded positions. The final diamond yieldachieved was 4 carats/cc. This yield was significantly higher thantypical commercial diamond synthesis processes providing less than 3carats/cc.

Example 4

Same as Example 3, except that each layer was made as a mixture of rawmaterial and catalyst material. The disks were made by blending a 1.5 to1 ratio of INVAR powder (having a grain size of about 40 microns) andgraphite powder and then pressing as before to make disks 1 mm inthickness. Ni coated diamond seeds were planted directly into thepressed disks using the same pattern template as before to form seededdisks. The seeded disks were stacked and pressed and heated to growdiamond. The results were substantially the same as Example 3.

Example 5

Same as Example 4, except the diamond seeds are uncoated, i.e. no Nicoating. The grown diamonds had poorer quality with black dots thatcorrespond to the original position of the crystalline seeds. Thecrystalline seeds had substantially back-converted to carbon. Thisexample highlights the desirability to surround diamond seeds withmolten catalyst before growth begins. In this case, graphite willdisperse across the molten catalyst envelope and precipitate out asdiamond. If the diamond is not fully enclosed by the molten catalyst asin the case of using an uncoated seed in a mixture, the directgraphite-diamond contact will result in highly visible graphiticinclusions.

Example 6

Same as Example 3, except the powder used in the mixture was iron havinga grain size of about 6 microns and cobalt having a grain size of about2 microns in a weight ratio of 2:1. Both nickel coated and uncoateddiamond seeds were used. As in other examples, the grown diamonds had apoorer quality when using uncoated diamond seeds.

Example 7

A substantially homogenous mixture of natural graphite (20 microns) andINVAR powder (40 microns) at a 1:1.5 weight ratio were pressed at 350MPa to form disks of 37 mm in diameter and 1 mm thick. The surface ofthese disks was sprayed with a thin arcrylic binder. A template withholes 130 microns in diameter separated at 800 microns was placeddirectly on top of the binder. Diamonds (60 microns) that were coatedwith nickel to a size of about 120 microns were swept across the topsurface of the template. Diamonds which enter each aperture are adheredto the binder on the disk. After the removal of the excess diamond andthe template, the diamond implanted disks were stacked up to about 30layers and then were placed in a steel container with one open end. Theopen cans were then heated to 600° C. for two hours to remove thebinder. Subsequently, another steel container was used to cover the openend and the two containers pressed at 30 tons force to become tightlyheld. The can is then subjected to ultrahigh pressure of 5.2 GPa and1300° C. for 50 minutes. The result showed grid distribution of diamondcrystals of 30/40 mesh with negligible amount of spontaneous nucleation.The clean diamond showed yellow color and with high impact strength.

Example 8

Same as Example 7, except the diamond seeds were first adhered to aflexible tape using the template. The patterned diamond seeds were thentransferred to the binder coated disks. The binder on the disk isstronger than the adhesive on the tape such that diamond particles weretransferred with ease. The results were substantially the same as inExample 7.

Example 9

Same as Example 1, except the diamond seeds are adhered to a thin nickellayer (37 mm by 0.08 mm thick). The metal layer was much easier tohandle during the patterned seeding process than pressed disks. Themetal layer was then sandwiched between pressed disks of graphite andINVAR mixture. Yellow diamond crystals formed after the high pressuresynthesis similar to Example 7.

Example 10

Uncoated diamond seeds (30 microns) were used adhered on a nickel diskusing a template. The resulting grown diamonds had slightly moreinclusions than Example 7, but were still yellow with high impactstrength.

Example 11

The above examples can be substituted with pure graphite disks that arestacked with INVAR disks. In this case, diamond seeds adhere to theINVAR disk.

Example 12

FIG. 19A is a photomicrograph of a post-growth mass using conventionaldiamond growth technologies which involve forming a mixture of rawmaterial and catalyst material. The growth conditions for this samplewere a pressure of 5.2 GPa and a temperature of 1300° C. for 35 minutes.FIG. 19B is a photomicrograph of unsorted and unsized diamonds asrecovered from the mass of FIG. 19A. The recovered diamonds werecubo-octahedral having a wide size distribution and poor quality. Theoverall diamond yield for this cell was about 2 ct/cc.

In accordance with the present invention, diamond seeds having anaverage size of 65 μm were coated with nickel to a final diameter ofabout 125 μm (e.g., see FIGS. 8A and 8B). The coated diamond seeds werearranged in a powdered mixture of graphite and INVAR (65Fe-35Ni) at aratio of 1:1.5 using a template as described above and a multi-layeredconfiguration similar to that shown in FIG. 17. Two separatemulti-layered precursors were prepared in this manner.

FIG. 20A is a photomicrograph of a post-growth mass formed by pressingone of the multi-layered precursors at 5.2 GPa and heating to 1300° C.for 35 minutes. FIG. 20B is a photomicrograph of unsorted and unsizeddiamonds recovered from the mass of FIG. 20A. The recovered diamondswere cubo-octahedral having a highly uniform size and qualitydistribution characterized by very few inclusions and a yellow color.The overall diamond yield for this cell was about 5 ct/cc.

FIG. 21A is a photomicrograph of a post-growth mass formed by pressingone of the multi-layered precursors at 5.2 GPa and heating to 1320° C.for 35 minutes. FIG. 21B is a photomicrograph of unsorted and unsizeddiamonds recovered from the mass of FIG. 21A. The recovered diamondswere octahedral having a highly uniform size and quality distributioncharacterized by very few inclusions and a yellow color. The overalldiamond yield for this cell was about 5 ct/cc.

Each of FIGS. 19B, 20B and 21B is illustrated at the same enlargementscale. Thus, it can be seen that the average size of the diamonds usingthe present invention is larger than those using conventional seedingprocesses, as well as more uniform in crystal morphology and quality.

Example 13

Diamond crystals with faceted morphology or blocky shape having a sizefrom 20-30 microns were coated with nickel via an electroless process toa size of 60-70 microns. Purified natural graphite powder having a grainsize of about 20 microns was mixed with INVAR (Fe65-Ni35) powder havinga size of about 40 microns at a weight ratio of 1:1. The mixture waspressed at about 200 MPa to form disks of 0.9 mm in thickness of variousdiameters, e.g. 37 mm, 61 mm, and 85 mm. A screen printer was used tospread the nickel coated diamond seeds over an adhesive pad(manufactured by 3M) of uniform thickness (1, 2, or 3 mils). Theadhesive adheres to the screen that contains a predetermined grid ofholes 0.9 mm apart. These holes allow coated diamond crystals to besecured on the adhesive pad to form the same predetermined pattern.

After removal of excess diamond crystals, the diamond grid formed on theadhesive pad is removed from the backing layer and glued to the pressedgraphite-metal disks. The gluing may be on the back side of the adhesivepad opposite the diamond seeds or on the same side where diamond seedsare attached. Multiple layers (e.g. 40) of graphite-metal disks andpatterned diamond seeds were stacked up in a steel container having awall thickness of about 0.2 mm to form a multilayered precursorassembly. The precursor assembly was heat treated under vacuum (10ˆ-3torr) at 1000° C. for 60 minutes with intermittent hydrogen purges.During cooling the stacks were purged under nitrogen gas.

The pretreated stacks were compressed at about 300 MPa to form cells forultrahigh pressure synthesis of diamond. Subsequently, the pretreatedstacks were pressed at 5.2 GPa and heated to 1300° C. for 45 minutes.The grown diamonds were recovered and examined. The diamond seeds grewto about 500 microns (30/40 mesh) with uniform size and similar shape asshown in FIGS. 22 through 26. These diamond crystals were grown withhigh crystal perfection and mechanical strength. The yield of diamondwas over 4 carats per cubic centimeter.

FIG. 23 is a photograph of a post-growth mass having offset patterns ofdiamond crystals to allow more growing space for each crystal. Thispattern was achieved by rotating either the screen during screenprinting or rotating the adhesive pad prior to gluing to the disks. Thisrotational arrangement can be easily automated and can allow tighterpacking of diamond seeds in the space of the high pressure cell withoutinterference from the diamond crystals directly above and below adjacentlayers.

FIG. 24 is a photomicrograph of the post-growth mass of diamondparticles having a predominantly cubic morphology and an average size ofabout 500 μm as indicated by the bracket.

FIG. 25 is an additional photomicrograph of the post-growth mass showingcubic diamonds prior to recovery. These diamonds show a high degree ofuniformity in quality, size and morphology which is uncharacteristic ofconventional diamond synthesis processes. FIG. 26 illustrates acollection of unsorted diamonds having a predominantly cubic morphologyproduced from this example.

Example 14

The same conditions and steps were performed as in Example 13 with INVARpowder being replaced by pure Fe and Ni powder (about 6 microns) at a2:1 weight ratio. The resulting grown diamond was of substantially thesame quality and sizes.

Example 15

The same conditions and steps were performed as in Example 13 exceptthat the heating time is extended to one hour so the diamond sizeincreased to over 600 microns (25/30 mesh). Also, the diamond yield wasover 5 carats/cubic centimeter with similar quality as in Example 14.

Thus, there is disclosed an improved method and materials for making andgrowing superabrasive particles with improved quality and sizedistributions. The above description and examples are intended only toillustrate certain potential embodiments of this invention. It will bereadily understood by those skilled in the art that the presentinvention is susceptible of a broad utility and applications. Manyembodiments and adaptations of the present invention other than thoseherein described, as well as many variations, modifications andequivalent arrangements will be apparent from or reasonably suggested bythe present invention and the forgoing description thereof withoutdeparting from the substance or scope of the present invention.Accordingly, while the present invention has been described herein indetail in relation to its preferred embodiment, it is to be understoodthat this disclosure is only illustrative and exemplary of the presentinvention and is made merely for purpose of providing a full andenabling disclosure of the invention. The foregoing disclosure is notintended or to be construed to limit the present invention or otherwiseto exclude any such other embodiment, adaptations, variations,modifications and equivalent arrangements, the present invention beinglimited only by the claims appended hereto and the equivalents thereof.

1. A method for synthesizing superabrasive particles, comprising thesteps of: providing a growth precursor including a raw material and acatalyst material, and having crystalline seeds arranged at leastpartially therein; selecting a temperature profile that promotessuperabrasive particle growth in either octahedral or cubic shape; andgrowing the superabrasive particles under pressure and the selectedtemperature profile in order to grow superabrasive particles having apreselected morphology.
 2. The method of claim 1, wherein thetemperature profile includes elevating the temperature to a set-pointand maintaining the temperature at the set-point for the duration ofprocessing.
 3. The method of claim 1, wherein the temperature profileincludes more than one processing temperature.
 4. The method of claim 3,wherein the temperature profile includes step-wise adjustments totemperature.
 5. The method of claim 3, wherein the temperature profileincludes continuous adjustments to temperature.
 6. The method of claim1, wherein the temperature profile is selected to promote asubstantially even relative growth rate perpendicular to (100) and (111)faces.
 7. The method of claim 1, wherein the temperature profile isselected to promote growth perpendicular to an (111) face.
 8. The methodof claim 7, wherein the temperature profile includes a set-point ofabout 1250° C. to about 1310° C.
 9. The method of claim 7, wherein thepreselected morphology is dominantly cubic or cubo-octahedral.
 10. Themethod of claim 7, wherein greater than about 70% of the superabrasiveparticles are cubic.
 11. The method of claim 1, wherein the temperatureprofile is selected to promote growth perpendicular to an (100) face.12. The method of claim 11, wherein the temperature profile includes aset-point of about 1305° C. to about 1320° C.
 13. The method of claim11, wherein the preselected morphology is dominantly octahedral.
 14. Themethod of claim 11, wherein greater than about 70% of the superabrasiveparticles are octahedral.
 15. The method of claim 1, wherein thetemperature profile is adjusted based on the crystalline seedmorphology.
 16. The method of claim 1, wherein the superabrasiveparticles are diamond and the raw material is a carbon source.
 17. Themethod of claim 1, wherein the pressure is constant.
 18. A method forcontrolling superabrasive particle shape during growth from crystallineseeds under high pressure and temperature conditions, comprisingutilizing a temperature selected to direct growth of superabrasiveparticles in either an octahedral or a cubic morphology.
 19. The methodof claim 18, wherein the morphology is cubic and the temperatureselected to direct growth of superabrasive particles is about 1250° C.to about 1310° C.
 20. The method of claim 18, wherein the morphology isoctahedral and the temperature selected to direct growth ofsuperabrasive particles is about 1305° C. to about 1320° C.
 21. Themethod of claim 18, wherein the superabrasive particles are diamond.